Expansible polystyrene resin particles, method for producing the same, styrenic resin foam particles and foam particle molded article

Abstract

To provide foamable styrenic resin particles which enable production of a styrenic resin foam particle molding having good cutting workability, a method for producing the same, styrenic resin foam particles, and a foam particle molding.SOLUTION: A method for producing foamable styrenic resin particles includes a polymerization step of suspension-polymerizing a styrenic monomer in the presence of a polyethylene wax, and thereby obtaining styrenic resin particles. A melting point of the polyethylene wax is 90°C or higher and 120°C or lower. A crystallization heat quantity of the polyethylene wax calculated based on a DSC curve is 225 J / g or more. An amount of the polyethylene wax to be added in the polymerization step is 0.02 pts.mass or more and 0.2 pts.mass or less with respect to 100 pts.mass of the styrenic monomer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to expandable styrene-based resin beads, a method for producing the same, expanded styrene-based resin beads, and expanded bead molded articles. [Background technology]

[0002] Expanded styrene resin bead molded articles obtained by molding expanded styrene resin beads in a mold are lightweight and have excellent compression properties, and therefore are used in various fields such as automotive materials, construction materials, logistics materials, etc. Expanded styrene resin bead molded articles are also used as lost patterns for casting (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-199548 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the expanded bead molded article made of styrene-based resin expanded beads of Patent Document 1 is cut or machined, the smoothness of the surface of the molded article exposed by the cutting or machining may decrease. More specifically, the surface of the molded article is prone to fuzzing caused by cutting the expanded beads and depressions caused by falling off of the expanded beads, which may deteriorate the appearance and feel of the exposed cross section. Such a decrease in smoothness is particularly likely to occur when cutting or machining a large molded article, such as a block molded article having a rectangular parallelepiped shape.

[0005] Furthermore, when the molded body is used as a lost pattern for casting, if the surface smoothness of the molded body after cutting is reduced as described above, it may be difficult to obtain a metal product with a good surface.

[0006] The present invention has been made in view of such a background, and aims to provide expandable styrene-based resin particles capable of obtaining a styrene-based resin foam particle molded body with good machinability, a method for producing the same, styrene-based resin foam particles, and a foam particle molded body.

Means for Solving the Problems

[0007] One aspect of the present invention is a method for producing expandable styrene-based resin particles containing a styrene-based resin, a foaming agent, and polyethylene wax, including a polymerization step of obtaining styrene-based resin particles by suspension polymerization of a styrene-based monomer in the presence of polyethylene wax, wherein the melting point of the polyethylene wax is 90°C or higher and 120°C or lower, the heat of crystallization of the polyethylene wax calculated based on the DSC curve is 225 J / g or higher, and the addition amount of the polyethylene wax in the polymerization step is 0.02 parts by mass or more and 0.2 parts by mass or less with respect to 100 parts by mass of the styrene-based monomer. The method for producing expandable styrene-based resin particles is provided.

Effects of the Invention

[0008] According to the expandable styrene-based resin particles (hereinafter referred to as "expandable particles") obtained by the production method of the above aspect, styrene-based resin foam particles (hereinafter referred to as "foam particles") capable of producing a styrene-based resin foam particle molded body (hereinafter referred to as "foam particle molded body" or "molded body") with good machinability can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] (Method for Producing Expansible Polystyrene Resin Particles) The production method has a polymerization step of obtaining styrene resin particles by suspension polymerization of a styrene monomer in the presence of polyethylene wax. Further, by impregnating the styrene resin particles with a foaming agent, expansible styrene resin particles can be obtained. Hereinafter, specific embodiments of the production method will be described in detail.

[0011] ·Polymerization Step In the polymerization step, styrene resin particles (hereinafter referred to as "resin particles") are produced by suspension polymerization of a styrene monomer in the presence of polyethylene wax. More specifically, an aqueous medium such as water is introduced into a sealed container equipped with a stirring device. Next, a suspending agent and a surfactant are introduced into the sealed container as necessary. After suspending a styrene monomer containing polyethylene wax and a polymerization initiator in this aqueous medium, the polymerization reaction is started. Thereby, styrene resin can be used as a base resin, and styrene resin particles containing polyethylene wax can be obtained. In addition, at the time of suspension polymerization, it is preferable to suspend a styrene monomer in which polyethylene wax and a polymerization initiator are previously dissolved in an aqueous medium and carry out the polymerization.

[0012] The polymerization step may include a pre-polymerization step of polymerizing a styrene monomer at a first polymerization temperature and a post-polymerization step of polymerizing the styrene monomer at a second polymerization temperature higher than the pre-polymerization temperature. The pre-polymerization step is a step of polymerizing most of the styrene monomer at a relatively low temperature to obtain a styrene resin, and the post-polymerization step is a step of polymerizing the remaining unreacted styrene monomer. By performing the polymerization of the styrene monomer in two steps in this way, it is possible to more easily obtain styrene resin particles having desired properties and a low content of unreacted styrene monomer.

[0013] The polymerization temperature in the pre-polymerization step is preferably 110°C or lower, and more preferably 105°C or lower. In this case, the weight-average molecular weight of the styrene resin can be appropriately increased. By molding the foamed particles composed of such a styrene resin in a mold, the mechanical strength of the foamed particle molded body can be further improved. On the other hand, from the viewpoint of polymerization efficiency, the lower limit of the polymerization temperature in the pre-polymerization step is approximately 70°C. Also, the holding time of the polymerization temperature in the pre-polymerization step may be, for example, 3 hours or more, and preferably 4 hours or more. From the viewpoint of enhancing productivity, the holding time of the polymerization temperature in the pre-polymerization step is preferably 6 hours or less, and more preferably 5 hours or less.

[0014] Also, from the viewpoint of further reducing the unreacted styrene monomer, in the pre-polymerization step, it is preferable to perform the polymerization until the polymerization conversion rate of the styrene monomer reaches 90% by mass or more, more preferably until it reaches 95% by mass or more, and even more preferably until it reaches 98% by mass or more.

[0015] In the post-stage polymerization step, the polymerization temperature is preferably higher than 115°C and not higher than 135°C, more preferably 118°C or higher and 130°C. In this case, unreacted styrene-based monomers can be further reduced. The amount of unreacted styrene-based monomers in the post-stage polymerization step can be controlled by the holding time at the final polymerization temperature. The holding time of the polymerization temperature in the post-stage polymerization step may be, for example, 1 hour or more, preferably 1.5 hours or more. Also, from the viewpoint of enhancing productivity, the holding time of the polymerization temperature in the pre-stage polymerization step is preferably 4 hours or less, more preferably 3 hours or less.

[0016] Further, in the post-stage polymerization step, it is preferable to polymerize the styrene-based monomer until the content of unreacted styrene-based monomers in the styrene-based resin becomes 2000 mass ppm or less, and more preferably until the content of unreacted styrene-based monomers becomes 1000 mass ppm or less.

[0017] The polymerization step preferably includes a step of polymerizing the styrene-based monomer at a temperature lower than the melting point of the polyethylene wax until the polymerization conversion rate reaches 90% by mass or more. When the polymerization step includes a pre-stage polymerization step and a post-stage polymerization step, it is preferable to polymerize the styrene-based monomer until the polymerization conversion rate reaches 90% by mass or more in the pre-stage polymerization step, more preferably until the polymerization conversion rate reaches 95% by mass or more, and even more preferably until the polymerization conversion rate reaches 98% by mass or more. By performing polymerization under such conditions, it becomes easier to obtain expandable particles having desired properties and to further reduce unreacted styrene-based monomers.

[0018] The method for measuring the polymerization conversion rate described above is as follows. First, perform the polymerization process until the time point at which the polymerization conversion rate is to be measured. Immediately after the polymerization process has progressed until the time point at which the polymerization conversion rate is to be measured, cool the temperature of the contents of the sealed container to 30°C or lower within 10 minutes to stop the polymerization reaction. That is, for example, when attempting to measure the polymerization conversion rate at the time when the previous polymerization step is completed, the contents of the sealed container may be rapidly cooled immediately after the previous polymerization step is completed to stop the polymerization reaction.

[0019] After the cooling is completed, remove the moisture adhering to the surface of the styrene-based resin particles taken out from the sealed container. As a method for removing moisture, for example, a method of dehydrating the styrene-based resin particles with a centrifuge or the like and then removing the moisture adhering to the surface of the styrene-based resin particles using a fluidized drying device or the like can be adopted. After the removal of moisture is completed, measure the content of the unreacted styrene-based monomer in the styrene-based resin particles by gas chromatography. The method for measuring the content of the styrene-based monomer by gas chromatography will be described later. The polymerization conversion rate (unit: mass%) is a value represented by the following mathematical formula (1). Polymerization conversion rate (unit: mass%) = 100 - content of styrene-based monomer (unit: mass%) ··· (1)

[0020] Examples of the styrene-based monomer used in the polymerization process include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-n-butylstyrene, p-t-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, divinylbenzene, styrenesulfonic acid, sodium styrenesulfonate, and the like. These styrene-based monomers may be used alone or in combination of two or more types of styrene-based monomers.

[0021] In addition, in the polymerization step, a monomer copolymerizable with styrene can also be added. Examples of monomers copolymerizable with styrene include acrylic esters and methacrylic esters. Examples of acrylic esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc. Examples of methacrylic esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, etc. These monomers may be used alone or in combination of two or more kinds.

[0022] From the viewpoint of easily obtaining expandable particles having desired properties, the proportion of styrene in all the monomers used in the polymerization step is preferably, for example, 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass, that is, using only styrene in the polymerization step.

[0023] The polyethylene wax used in the polymerization step is a relatively low molecular weight polyethylene composed of structural units derived from ethylene and is a solid wax under normal temperature and pressure (for example, 20 ° C, 1 atm). More specifically, the weight average molecular weight of the polyethylene wax is generally 300 or more and 10,000 or less. The melting point of the polyethylene wax is 90 ° C or more and 120 ° C or less, and the heat of crystallization of the polyethylene wax calculated based on the DSC curve is 225 J / g or more. By foaming expandable particles containing such a polyethylene wax, expandable particles with a small difference in bubble diameter between the bubbles present near the surface and the bubbles present inside the expandable particles can be obtained.

[0024] The reasons for obtaining foamed particles with a small variation in bubble diameter using the polyethylene wax are considered, for example, as follows. That is, it is considered that the polyethylene wax having a melting point and a crystallization heat amount within the specific range has an appropriate solubility in the styrene-based monomer. Therefore, for some time after the start of the polymerization process, the polyethylene wax is dissolved in the styrene-based monomer. On the other hand, as the polymerization reaction of the styrene-based monomer proceeds, the polyethylene wax gradually precipitates in the styrene-based resin, and it is considered that the precipitates of the polyethylene wax can be dispersed almost evenly in the styrene-based resin.

[0025] The precipitates of the polyethylene wax dispersed in the styrene-based resin function as a nucleating agent that serves as a starting point for bubble formation. Therefore, when the foaming particles are foamed, bubbles are likely to be formed almost evenly throughout the particles. As a result, it is considered that foamed particles with a small difference in bubble diameter between the bubbles existing near the surface of the foamed particles and the bubbles existing inside the foamed particles can be obtained.

[0026] In addition, since such foamed particles have excellent fusibility during in-mold molding, a molded body with less dropout of foamed particles during cutting can be easily obtained. Furthermore, such foamed particles have a small difference between the structure in the central part of the particles and the structure in the surface layer part. Therefore, by molding such foamed particles in a mold, a molded body with less fluffing after cutting can be easily obtained.

[0027] When the melting point of the polyethylene wax is too low, it becomes difficult for the polyethylene wax to precipitate in the styrene-based resin, so the effect as a nucleating agent decreases. As a result, the variation in bubble diameter of the bubbles in the foamed particles is likely to increase. Also, in this case, it may lead to a decrease in the fusibility of the foamed particles, and there is a possibility that a portion with insufficient fusion between the foamed particles may be easily formed in the molded body. And when a portion with insufficient fusion between the foamed particles is formed in the molded body, there is a possibility that the foamed particles may easily drop off from this portion during cutting.

[0028] On the other hand, if the melting point of the polyethylene wax is too high, the precipitation of the polyethylene wax during the polymerization process tends to be unstable. As a result, the variation in the cell diameter of the bubbles in the foamed particles tends to be large. Also, in this case, it may lead to a decrease in the fusion property of the foamed particles, and there is a possibility that a portion where the foamed particles are insufficiently fused to each other is likely to be formed in the molded body. And when a portion where the foamed particles are insufficiently fused to each other is formed in the molded body, there is a possibility that the foamed particles are likely to fall off from this portion during cutting.

[0029] From the viewpoint of more surely avoiding these problems and more easily obtaining the desired foaming particles, the melting point of the polyethylene wax is preferably 95 °C or higher, more preferably 100 °C or higher, and even more preferably 105 °C or higher. From the same viewpoint, the melting point of the polyethylene wax is preferably 115 °C or lower.

[0030] The weight average molecular weight of the polyethylene wax is preferably 1000 or more, preferably 1500 or more, and preferably 2000 or more. In this case, the polyethylene wax is likely to be appropriately precipitated in the styrene resin. Also, the weight average molecular weight of the polyethylene wax is preferably 8000 or less, more preferably 5000 or less, and even more preferably 4000 or less. In this case, the polyethylene wax is likely to be well dispersed in the styrene resin.

[0031] If the heat of crystallization of the polyethylene wax is too low, the cell diameter of the bubbles existing near the surface of the foamed particles tends to be small. This is presumably because the polyethylene wax is likely to precipitate in the styrene resin during the polymerization process, and the amount of the polyethylene wax precipitating near the surface of the foaming particles tends to be large.

[0032] If the bubble diameter in the surface layer of the expanded particles is too small compared to the average diameter of the bubbles in the entire expanded particles, the surface layer of the expanded particles cannot be completely removed after machining the molded body, and fuzzing is likely to occur. Furthermore, in this case, the fusibility of the expanded particles decreases, and there is a risk of causing the dropout of the expanded particles with insufficient fusion when machining the molded body. Although the upper limit of the crystallization heat quantity of the polyethylene wax is not particularly limited, for example, it may be about 280 J / g, and preferably 250 J / g.

[0033] The melting point of the polyethylene wax described above can be determined based on the differential scanning calorimetry (that is, DSC) performed in accordance with JIS K7121-1987 and based on the obtained DSC curve. The method for obtaining the DSC curve used for determining the melting point of the polyethylene wax is specifically as follows. First, the state adjustment of the polyethylene wax is performed in accordance with “(2) After performing a certain heat treatment, when measuring the melting temperature”. In the state adjustment, the polyethylene wax is heated from 0 °C to 150 °C at a heating rate of 10 °C / min, and then the temperature of 150 °C is held for 10 minutes to melt the polyethylene wax. Next, the polyethylene wax is cooled from 150 °C to 0 °C at a cooling rate of 10 °C / min. After performing the state adjustment as described above, the polyethylene wax is heated from 0 °C to 150 °C at a heating rate of 10 °C / min, and the DSC curve during the second temperature increase is obtained. Then, the peak of the melting peak appearing in the DSC curve during the second temperature increase is taken as the melting point of the polyethylene wax. In the DSC curve, when multiple melting peaks appear, the peak temperature of the melting peak appearing on the highest temperature side is taken as the melting point of the polyethylene wax.

[0034] In addition, the heat of crystallization of the polyethylene wax described above can be calculated based on the DSC curve obtained by performing DSC in accordance with JIS K7122-1987. The method for obtaining the DSC curve used for calculating the heat of crystallization of the polyethylene wax is specifically as follows. First, the state of the polyethylene wax is adjusted according to "(2) When measuring the melting temperature after performing a certain heat treatment". In the state adjustment, the polyethylene wax is heated from 0 °C to 150 °C at a heating rate of 10 °C / min, and then the temperature of 150 °C is held for 10 minutes to melt the polyethylene wax. After the state adjustment is performed as described above, the polyethylene wax is cooled from 150 °C to 0 °C at a cooling rate of 10 °C / min, and the DSC curve during cooling is obtained. Then, the area of the crystallization peak appearing in the DSC curve during cooling is calculated, and the heat of crystallization is calculated from this value.

[0035] The addition amount of the polyethylene wax in the polymerization step is 0.02 parts by mass or more and 0.2 parts by mass or less with respect to 100 parts by mass of the styrene-based monomer. Thereby, the above-described effects can be exhibited. When the addition amount of the polyethylene wax is too small, the effect as a nucleating agent of the polyethylene wax becomes insufficient, and the variation in the cell diameter of the cells in the foamed particles tends to increase. Further, in this case, a decrease in the fusion property of the foamed particles is caused, and when the molded body is machined by cutting, there is a risk that the foamed particles are likely to fall off from the portion where the fusion of the foamed particles is insufficient. From the viewpoint of more surely obtaining the effects of the polyethylene wax, the addition amount of the polyethylene wax in the polymerization step is preferably 0.04 parts by mass or more, more preferably 0.06 parts by mass or more, and even more preferably 0.08 parts by mass or more with respect to 100 parts by mass of the styrene-based monomer.

[0036] On the other hand, when the addition amount of the polyethylene wax is too large, the number of polyethylene waxes precipitating in the expandable particles becomes excessively large, and the bubble diameter of the bubbles near the surface of the expandable particles tends to be small. Also, in this case, the fusion property of the expandable particles is reduced, and when machining the molded body, there is a risk that the expandable particles are likely to fall off from the portions where the fusion between the expandable particles is insufficient. From the viewpoint of more reliably avoiding such problems, the addition amount of the polyethylene wax is preferably 0.18 parts by mass or less, more preferably 0.16 parts by mass or less, and even more preferably 0.14 parts by mass or less with respect to 100 parts by mass of the styrene-based monomer.

[0037] The half-value width of the crystallization peak of the polyethylene wax is preferably 6°C or more and 30°C or less. In this case, the deviation of the distribution of the polyethylene wax in the expandable particles becomes moderately small, and a molded body excellent in fusion property and machinability can be more easily obtained. From the viewpoint of further enhancing such effects, the half-value width of the crystallization peak of the polyethylene wax is more preferably 25°C or less, even more preferably 20°C or less, and particularly preferably 15°C or less. Also, the half-value width of the crystallization peak of the polyethylene wax is more preferably 7°C or more, and more preferably 8°C or more.

[0038] Also, the crystallization peak temperature of the polyethylene wax is preferably 90°C or more and 105°C or less. In this case, the polyethylene wax is likely to precipitate moderately during the polymerization process, and a molded body excellent in fusion property and machinability can be more reliably obtained. From the viewpoint of further enhancing such effects, the crystallization peak temperature of the polyethylene wax is more preferably 93°C or more, even more preferably 96°C or more, and particularly preferably 100°C or more.

[0039] The crystallization peak temperature and the half-width of the polyethylene wax can be calculated based on the DSC curve obtained by performing DSC in accordance with JIS K7121-1987. The method for obtaining the DSC curve used for calculating the crystallization peak temperature and the half-width of the polyethylene wax is specifically as follows. First, condition the polyethylene wax according to "(2) When measuring the melting temperature after performing a certain heat treatment". In the conditioning, heat the polyethylene wax from 0°C to 150°C at a heating rate of 10°C / min, and then hold the temperature of 150°C for 10 minutes to melt the polyethylene wax. After conditioning as above, cool the polyethylene wax from 150°C to 0°C at a cooling rate of 10°C / min to obtain a DSC curve during cooling. Then, take the temperature corresponding to the peak of the crystallization peak appearing in the DSC curve during cooling as the crystallization peak temperature. Also, in the DSC curve during cooling, obtain the height from the baseline to the peak of the DSC curve and take this value as the crystallization peak height. Next, determine two points on the DSC curve where the height from the baseline is half of the crystallization peak height, and set these points as the 1 / 2 crystallization peak height positions. Then, take the difference between the temperatures corresponding to these two 1 / 2 crystallization peak height positions, that is, the value obtained by subtracting the temperature corresponding to the 1 / 2 crystallization peak height position on the low-temperature side from the temperature corresponding to the 1 / 2 crystallization peak height position on the high-temperature side as the half-width of the crystallization peak. Note that a line segment connecting the point of [crystallization start temperature + 10°C] and the point of [crystallization end temperature - 10°C] in the DSC curve can be defined as the baseline used for calculating the half-width.

[0040] The polyethylene wax used in the polymerization step may be in powder form or in granular form. From the viewpoint of enhancing the solubility in the styrene monomer, the volume-based median diameter (i.e., d50) of the polyethylene wax is preferably 35 μm or more and 200 μm or less, more preferably 40 μm or more and 120 μm or less, and even more preferably 50 μm or more and 100 μm or less. In this case, the distribution of the polyethylene wax in the styrene resin tends to be more uniform, so that desired foamed particles can be stably obtained more easily. Also, from the same viewpoint, the ratio of the difference between the volume-based d90 particle diameter (i.e., d90) and the volume-based d10 particle diameter (i.e., d10) of the polyethylene wax to the median diameter ([d90 - d10] / d50) is preferably 2.0 or more and 3.0 or less.

[0041] In the polymerization step, a plasticizer may be added to the styrene monomer. Examples of the plasticizer include liquid paraffin, glycerin diacetomonolaurate, glycerin tristearate, di-2-ethylhexyl phthalate, di-2-ethylhexyl adipate, and the like.

[0042] It is preferable to use liquid paraffin as the plasticizer. In this case, the addition amount of the liquid paraffin is preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the styrene monomer. By adding liquid paraffin to the styrene monomer, the fusion property of the foamed particles can be further enhanced. As a result, even when forming a large molded article, the fusion of the foamed particles inside is good, and a molded article excellent in cutting processability can be easily obtained. In this specification, liquid paraffin refers to paraffin that is liquid under normal temperature and pressure (for example, 20 °C, 1 atm). As the liquid paraffin, the liquid paraffin defined in JIS K 2231:1993 can be preferably used.

[0043] In addition, in the polymerization step, additives such as a chain transfer agent, an antistatic agent, an antioxidant, an ultraviolet absorber, and a light stabilizer may be further added to the styrene monomer within a range that does not impair the above-described effects.

[0044] As the chain transfer agent, for example, octyl mercaptan, dodecyl mercaptan, α-methylstyrene dimer, etc. can be used. As the antistatic agent, alkyldiethanolamine, glycerin fatty acid ester, sodium alkyl sulfonate, etc. can be used.

[0045] As the antioxidant, phenolic, phosphorus-based, sulfur-based antioxidants, etc. can be used. As the ultraviolet absorber, benzotriazole-based, benzophenone-based ultraviolet absorbers, etc. can be used. As the light stabilizer, hindered amine-based light stabilizers, etc. can be used.

[0046] As the polymerization initiator in the polymerization step, an organic peroxide can be used. When the polymerization step includes a pre-polymerization step and a post-polymerization step, as the polymerization initiator used in the pre-polymerization step, for example, an organic peroxide having a 10-hour half-life temperature of 65°C or higher and 90°C or lower can be used. Also, as the polymerization initiator used in the post-polymerization step, for example, an organic peroxide having a 10-hour half-life temperature exceeding 90°C and 110°C or lower can be used.

[0047] More specifically, in the first-stage polymerization step, for example, organic peroxides such as t-butyl peroxy-2-ethylhexanoate, t-hexyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, t-amyl peroxy-2-ethylhexanoate, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-2-methylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane can be used as polymerization initiators. These organic peroxides may be used alone or in combination of two or more organic peroxides.

[0048] In addition, in the second-stage polymerization step, organic peroxides such as t-butyl peroxy-2-ethylhexyl carbonate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate, t-amyl peroxy-2-ethylhexyl carbonate, t-hexyl peroxyacetate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(t-butylperoxy)butane can be used as polymerization initiators. These organic peroxides may be used alone or in combination of two or more organic peroxides.

[0049] The addition amount of the organic peroxide is preferably 0.01 part by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the styrene monomer. In this case, while suppressing an increase in production cost associated with the usage amount of the organic peroxide, the polymerization rate can be increased to sufficiently enhance productivity. From the same viewpoint, the addition amount of the organic peroxide is more preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the styrene monomer.

[0050] When t-butyl peroxy-2-ethylhexanoate is used as the polymerization initiator in the pre-stage overlapping process, it is preferable to add a polymerization inhibitor to the aqueous medium within a range that does not inhibit the polymerization of the styrene-based monomer. In this case, the variation in the average particle diameter of the expandable particles can be reduced. Examples of the polymerization inhibitor include oil-soluble polymerization inhibitors such as 4-t-butylcatechol (p-TBC), hydroquinone, p-benzoquinone, chloro-p-benzoquinone, 2,5-dichlorobenzoquinone, 2,6-dichlorobenzoquinone, 2,3-dimethyl-p-benzoquinone, 2,5-dimethyl-p-benzoquinone, methoxy-p-benzoquinone, tetrabromo-p-benzoquinone, tetrachloro-p-benzoquinone, dimethyl-p-benzoquinone, o-dinitrobenzene, m-dinitrobenzene, p-dinitrobenzene, 2,4-dinitrotoluene, 1,3,5-trinitrobenzene, 1,3,5-trinitroanisole, 2,4,6-trinitrophenol; and water-soluble polymerization inhibitors such as sodium nitrite, potassium nitrate, ammonium nitrite, L-ascorbic acid, and citric acid.

[0051] The timing of adding the polymerization inhibitor is not particularly limited. However, when using an oil-soluble polymerization inhibitor, it is preferable to add the styrene-based monomer in which the polymerization initiator and the polymerization inhibitor are dissolved to the aqueous medium in the polymerization process. The addition amount of the polymerization inhibitor is preferably 0.0001 parts by mass or more and 0.01 parts by mass or less with respect to 100 parts by mass of the styrene-based monomer.

[0052] In the polymerization step, a suspending agent and / or a surfactant can be added to the aqueous medium as necessary. That is, in the polymerization step, the polymerization of the styrene-based monomer can be carried out in a dispersion medium such as water to which a suspending agent and / or a surfactant is added. As the suspending agent, for example, hydrophilic polymers such as polyvinyl alcohol, methyl cellulose, and polyvinyl pyrrolidone, and hardly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, aluminum oxide, talc, kaolin, and bentonite can be used. Further, as the surfactant, for example, anionic surfactants such as sodium alkyl sulfonate and sodium dodecylbenzenesulfonate can be used. On the other hand, from the viewpoint of easily obtaining a molded article with good internal fusion even when molding a large molded article, it is preferable to carry out the polymerization step without adding a surfactant to the aqueous medium.

[0053] The amount of the suspending agent used is preferably 0.01 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the styrene-based monomer. When a suspending agent composed of a hardly water-soluble inorganic salt and an anionic surfactant are used in combination, with respect to 100 parts by mass of the styrene-based monomer, it is preferable to use 0.05 part by mass or more and 3 parts by mass or less of the suspending agent and 0.0001 part by mass or more and 0.5 part by mass or less of the anionic surfactant.

[0054] ·Foaming agent impregnation step In the manufacturing method, expandable resin particles can be obtained by performing a foaming agent impregnation step of impregnating the styrene-based resin particles with a foaming agent. The foaming agent impregnation step may be carried out at any timing as long as the foaming agent can be impregnated into the styrene-based resin particles. For example, in the manufacturing method, the foaming agent impregnation step may be started simultaneously with the polymerization step or during the polymerization step, and the resin particles in the middle of polymerization may be impregnated with the foaming agent. Further, the foaming agent impregnation step may be started after the polymerization step is completed, and the resin particles after the polymerization is completed may be impregnated with the foaming agent. The number of times the foaming agent impregnation step is carried out may be once or two or more times.

[0055] When performing the foaming agent impregnation step in parallel with the polymerization step, it is preferable to start impregnating the resin particles with the foaming agent when the polymerization conversion rate of the styrene monomer is 80% by mass or more. In this case, since polymerization inhibition by the foaming agent is suppressed, the content of unreacted styrene in the resin particles can be reduced. From the viewpoint of further enhancing such an effect, it is more preferable to start impregnating the resin particles with the foaming agent when the polymerization conversion rate of the styrene monomer is 90% by mass or more, still more preferable when it is 95% by mass or more, and particularly preferable when it is 96% by mass or more. On the other hand, from the viewpoint of shortening the polymerization time and, for example, preventing the occurrence of surface depressions and improving the appearance of the molded article, in the foaming agent impregnation step, it is preferable to start impregnating the resin particles with the foaming agent when the polymerization conversion rate is 99.5% by mass or less. From the same viewpoint, it is more preferable to start impregnating the resin particles with the foaming agent when the polymerization conversion rate of the styrene monomer is 99% by mass or less.

[0056] When performing the foaming agent impregnation step, for example, the styrene resin particles can be impregnated with the foaming agent by adding the foaming agent into a sealed container. Further, the addition amount of the foaming agent in the foaming agent impregnation step may be, for example, an amount such that the foaming agent content in the foamable particles becomes 2 to 20% by mass.

[0057] As the foaming agent, for example, chain aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, normal hexane, and cyclic aliphatic hydrocarbons such as cyclohexane can be used. These foaming agents may be used alone or two or more kinds of foaming agents may be used in combination.

[0058] In the foaming agent impregnation step, it is preferable to use a foaming agent containing butane (including isomers) and pentane (including isomers), and having a mass ratio of pentane to butane of 0.1 or more and 0.6 or less. By foaming the expandable particles containing such a foaming agent, expandable particles having desired properties can be easily obtained. And according to such expandable particles, even when forming a large molded body, a molded body with good fusion between the expandable particles inside the molded body can be easily obtained.

[0059] (Expandable polystyrene resin particles) According to the manufacturing method, expandable polystyrene resin particles containing a styrene resin, a foaming agent, and polyethylene wax can be obtained. The expandable polystyrene resin particles contain 0.02 parts by mass or more and 0.2 parts by mass or less of polyethylene wax with respect to 100 parts by mass of the styrene resin. The melting point of the polyethylene wax is 90°C or more and 120°C or less, and the heat of crystallization of the polyethylene wax calculated based on the DSC curve is 225 J / g or more. In addition, the polyethylene wax is dispersed in the styrene resin.

[0060] By foaming the expandable particles, it is possible to easily obtain expandable particles with a small difference in bubble diameter between the bubbles present near the surface of the expandable particles and the bubbles present inside, and with little variation in bubble diameter. And according to such expandable particles, there is less dropout and fuzzing of the expandable particles during cutting, and a molded body having good machinability can be easily obtained.

[0061] The main component of the styrene resin constituting the expandable particles is a structural unit derived from the styrene monomer used in the polymerization step. The mass ratio of the structural unit derived from styrene in the styrene resin is preferably, for example, 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass, that is, the styrene resin is composed only of the structural unit derived from styrene.

[0062] The composition, function, and effect of the polyethylene wax in the expandable particles are the same as those of the polyethylene wax described in the manufacturing method mentioned above. Therefore, the description of the polyethylene wax in the manufacturing method can be referred to as appropriate.

[0063] From the perspective of more reliably obtaining the effect of the polyethylene wax, the content of the polyethylene wax is preferably 0.04 parts by mass or more, more preferably 0.06 parts by mass or more, and even more preferably 0.08 parts by mass or more with respect to 100 parts by mass of the styrene resin. On the other hand, from the perspective of more reliably avoiding the above-mentioned problems caused by excessive addition of the polyethylene wax, the content of the polyethylene wax is preferably 0.18 parts by mass or less, more preferably 0.16 parts by mass or less, and even more preferably 0.14 parts by mass or less with respect to 100 parts by mass of the styrene resin.

[0064] Also, the styrene resin in the expandable particles may contain additives such as plasticizers, chain transfer agents, antistatic agents, antioxidants, ultraviolet absorbers, and light stabilizers. Since these additives are the same as the additives in the manufacturing method, the description of the additives in the manufacturing method can be referred to as appropriate.

[0065] (Styrene resin expanded particles) By foaming the expandable styrene resin particles, styrene resin expanded particles using the styrene resin as the base resin can be obtained. As a method for foaming the expandable particles, for example, there is a method of heating the expandable particles using a heating medium such as steam.

[0066] The expandable styrene-based resin particles obtained by the suspension polymerization method are spherical. Therefore, the styrene-based resin expanded particles obtained by expanding the expandable styrene-based resin particles are also spherical. From the viewpoint of enhancing the filling property of the expanded particles into the mold and stably obtaining a molded body with good fusion between the expanded particles also inside the molded body, the average circularity of the expanded particles is preferably 0.90 or more, more preferably 0.95 or more, and even more preferably 0.98 or more. From the same viewpoint, the average aspect ratio of the expanded particles is preferably 1.10 or less, more preferably 1.05 or less, and even more preferably 1.03 or less.

[0067] The average circularity and average aspect ratio of the expanded particles can be measured, for example, using the particle size distribution measuring device "Millitrack JPA" manufactured by Nikkiso Co., Ltd. Specifically, first, about 5000 expanded particles are allowed to freely fall from the sample supply feeder of the measuring device, and the projection image is captured by a CCD camera. Next, the average circularity and average aspect ratio can be obtained by sequentially performing arithmetic processing and combining processing on the captured image information.

[0068] The bulk density of the styrene-based resin expanded particles is 15 kg / m 3 or more and 50 kg / m 3 or less, the coefficient of variation of the cell diameter of the styrene-based resin expanded particles is 40% or less, and the average value of the cell diameter of the cells present on the outermost surface of the styrene-based resin expanded particles is preferably 35 μm or more and 70 μm or less.

[0069] According to the styrene-based resin foam particles having the bulk density within the specific range, a molded article having suitable mechanical strength even when subjected to cutting and excellent flammability can be easily obtained. Further, in the foam particles, the coefficient of variation of the cell diameter and the average value of the cell diameters of the cells present on the outermost surface (hereinafter referred to as "surface layer cell diameter") are within the specific range, the difference between the cell diameters of the cells present in the surface layer portion and the cell diameters of the cells present inside is small, and the variation in cell diameter is small. Such foam particles have a small difference in structure between the surface layer portion and the interior, and thus are excellent in the fusion property between the foam particles and have a small difference in mechanical properties between the surface layer portion and the interior. Therefore, according to such foam particles, even when producing a large-sized molded article, the fusion between the foam particles inside the molded article is good, and a molded article excellent in machinability can be easily obtained.

[0070] When the bulk density of the foam particles is too low, the strength of the molded article becomes low, and for example, when the molded article is used as a lost foam pattern, it may be difficult to maintain the shape in the mold. On the other hand, when the bulk density of the foam particles is too high, there is a risk of increasing the density of the molded article. Further, in this case, for example, when the molded article is used as a lost foam pattern, the amount of gas generated during casting increases, which may lead to deterioration of castability.

[0071] The method for measuring the bulk density of the foam particles described above is as follows. First, the foam particles are filled into a graduated cylinder, and the filling height of the foam particles is stabilized at a predetermined position (for example, the 1 L mark). The value indicated by the mark at this time is taken as the bulk volume (unit: L) of the foam particles. Next, the mass (unit: g) of the foam particles in the graduated cylinder is measured. By dividing the mass of the foam particles thus obtained by the bulk volume and performing unit conversion, the bulk density (unit: kg / m 3 ) of the foam particles can be obtained.

[0072] When the coefficient of variation of the cell diameter of the expanded particles is too high, it causes a decrease in the fusion property of the expanded particles, and when producing a large molded body, the fusion between the expanded particles inside the molded body tends to be insufficient. Therefore, in this case, when performing cutting on the molded body, there is a risk that the expanded particles are likely to fall off. From the viewpoint of more surely avoiding such problems, the coefficient of variation of the cell diameter of the expanded particles is preferably 37% or less, more preferably 35% or less, and even more preferably 33% or less.

[0073] Also, when the average diameter of the surface layer cell diameter of the expanded particles is too small, the density of the surface layer portion of the expanded particles tends to become excessively high, and the difference between the structure in the surface layer portion and the structure inside the expanded particles tends to become large. Therefore, in this case, when cutting the molded body, there is a risk that fluffing is likely to occur when the expanded particles are cut. By setting the average value of the cell diameter of the bubbles present on the outermost surface of the styrene resin expanded particles to 35 μm or more, preferably 38 μm or more, and more preferably 40 μm or more, it is possible to make fluffing less likely to occur due to cutting.

[0074] On the other hand, when the average value of the cell diameter present on the outermost surface of the expanded particles is too large, there is a risk that the fusion property between the expanded particles decreases. In particular, when molding a large molded body, there is a risk that the fusion property inside the molded body decreases. By setting the average value of the cell diameter of the bubbles present on the outermost surface of the styrene resin expanded particles to 70 μm or less, preferably 60 μm or less, and more preferably 50 μm or less, such problems can be more easily avoided.

[0075] From the perspective of improving the machinability of the foamed particle molded body, the ratio of the average value of the bubble diameters of the bubbles present on the outermost surface of the foamed particles to the average diameter of the bubbles of the foamed particles is preferably 0.70 or more, more preferably 0.75 or more, and even more preferably 0.80 or more. On the other hand, from the perspective of easily enhancing the mechanical strength of the foamed particle molded body, the ratio of the average value of the bubble diameters of the bubbles present on the outermost surface of the foamed particles to the average diameter of the bubbles of the foamed particles is preferably 1.2 or less, and more preferably 1.1 or less.

[0076] The average diameter of the bubbles of the foamed particles is preferably 40 μm or more and 80 μm or less. Also, from the perspective of easily obtaining a lightweight molded body with excellent machinability, the ratio of the bulk density of the foamed particles to the average diameter of the bubbles of the foamed particles is preferably 2.0 or more, and more preferably 2.5 or more. Also, from the same perspective, the ratio of the bulk density of the foamed particles to the average diameter of the bubbles of the foamed particles is preferably 10 or less, more preferably 8.0 or less, and even more preferably 5.0 or less.

[0077] The method for calculating the average value of the surface layer bubble diameters of the foamed particles described above is as follows. First, the foamed particles are roughly divided into two equal parts by a cross-section passing through their central part, and the cut surface is exposed. Using a scanning electron microscope, a magnified photograph of the cut surface is taken. Next, the cut surface is divided into four parts, and one of the divided regions divided approximately every 90° with the center of the cut surface as the center point is selected. In the selected divided region, the longest diameter of all the bubbles located on the outermost surface of the foamed particles is measured. The value obtained by arithmetically averaging these longest diameters of the bubbles is defined as the surface layer bubble diameter (unit: μm) of each foamed particle.

[0078] The above operations are performed on 10 or more foamed particles to calculate the surface layer bubble diameter of each foamed particle. Then, the value obtained by arithmetically averaging these surface layer bubble diameters is defined as the average value of the surface layer bubble diameters of the foamed particles (unit: μm).

[0079] Also, the method for calculating the coefficient of variation of the bubble diameter of the foamed particles is as follows. First, divide the foamed particles into approximately two equal parts in the same way as when calculating the surface layer bubble diameter, and then take a magnified photograph of the cut surface with a scanning electron microscope. Next, randomly select 100 or more bubbles from the bubbles existing on the magnified photograph and measure the longest diameter of the selected bubbles. Then, the value obtained by arithmetically averaging these longest diameters is taken as the bubble diameter (unit: μm) of each foamed particle.

[0080] Perform the above operations on 10 or more foamed particles to calculate the bubble diameter of each foamed particle. Then, the value obtained by arithmetically averaging these bubble diameters is taken as the average diameter of the bubbles of the foamed particles (unit: μm). Furthermore, calculate the square root of the unbiased variance of the bubble diameters measured in the above-described operations, and take this value as the standard deviation of the bubble diameters of the foamed particles (unit: μm). The standard deviation of the bubble diameter is specifically the value calculated by the following formula (2). However, L in the following formula (2) sd is the standard deviation of the bubble diameter, n is the total number of bubbles whose bubble diameters were measured, L i is the bubble diameter of the i-th bubble (that is, the longest diameter of the bubble), L av is the average diameter of the bubbles.

[0081]

Equation

[0082] The value obtained by expressing the ratio of the standard deviation of the bubble diameter to the average diameter of the bubbles obtained above as a percentage is taken as the coefficient of variation of the bubble diameter (unit: %). That is, the coefficient of variation of the bubble diameter is specifically the value calculated by the following formula (3). Note that L in the following formula (3) cv is the coefficient of variation of the bubble diameter, L sd is the standard deviation of the bubble diameter, L av is the average diameter of the bubbles. L cv = L sd / L av × 100 ··· (3)

[0083] Since the styrene resin constituting the foamed particles is the same as the styrene resin constituting the expandable particles, the description of the styrene resin described above can be appropriately referred to.

[0084] The weight average molecular weight of the styrene resin is preferably more than 200,000 and 280,000 or less. In this case, the fusion property of the foamed particles can be further enhanced, and the foamed particles can be more reliably fused inside the molded body. Also, in this case, the mechanical strength of the molded body can be further enhanced.

[0085] The weight average molecular weight of the above-described styrene resin is the polystyrene-equivalent molecular weight measured by gel permeation chromatography using the foamed particles as a sample and polystyrene as a standard substance.

[0086] The ratio of the weight average molecular weight of the surface layer portion of the styrene resin foamed particles to the weight average molecular weight of the styrene resin foamed particles is preferably less than 1.03, more preferably 1.02 or less, and even more preferably 1.01 or less. In this case, the fusion property of the foamed particles can be further enhanced, and even when molding a large-sized molded body, the foamed particles inside the molded body can be more reliably fused. Also, according to such foamed particles, the machinability of the molded body can be further enhanced. Note that the lower limit of the ratio of the weight average molecular weight of the surface layer portion of the styrene resin foamed particles is, for example, 0.97, preferably 0.98, and more preferably 0.99.

[0087] The weight average molecular weight of the surface layer portion of the foamed particles is the polystyrene-equivalent molecular weight measured by gel permeation chromatography using, as a sample, a portion having a depth of 50 μm or less from the surface collected from the foamed particles and using polystyrene as a standard substance.

[0088] The styrene resin foam particles may contain polyethylene wax. In this case, the polyethylene wax is dispersed in the styrene resin. Since the polyethylene wax contained in the styrene resin foam particles is the same as the polyethylene wax contained in the expandable particles, the above description of the polyethylene wax can be referred to as appropriate.

[0089] The melting point of the polyethylene wax contained in the styrene resin foam particles is 90°C or higher and 120°C or lower, and the heat of crystallization of the polyethylene wax calculated based on the DSC curve is preferably 225 J / g or more. Since the foam particles containing the polyethylene wax are, for example, foam particles obtained by foaming the expandable particles, the coefficient of variation of the cell diameter and the average value of the surface layer cell diameter of the foam particles are likely to be foam particles within the specific range. From this perspective, it is preferable that the styrene resin foam particles contain 0.02 parts by mass or more and 0.2 parts by mass or less of polyethylene wax with respect to 100 parts by mass of the styrene resin.

[0090] (Foam particle molded body) By molding the foam particles in a mold, a foam particle molded body can be obtained. The in-mold molding of the foam particles is performed, for example, by the following method. First, a mold having a cavity with a shape corresponding to the desired shape of the molded body is prepared, and the foam particles are filled into the cavity. Then, a heating medium such as steam is supplied into the mold to heat the foam particles. The foam particles in the cavity expand while fusing with each other by heating. Thereby, the foam particles in the cavity are integrated, and a molded body having a shape corresponding to the cavity can be obtained.

[0091] After the heating of the foam particles is completed, the molded body is cooled in the mold until the shape of the molded body is stabilized to some extent. Then, the molded body may be removed from the mold.

[0092] The shape of the molded body may be appropriately set according to the intended use or the like. According to the foamed particles, even when molding a large molded body such as a rectangular parallelepiped-shaped foamed block, the foamed particles can be sufficiently fused to each other even inside the molded body. Therefore, the molded body is preferably a rectangular parallelepiped-shaped foamed block.

[0093] From the same perspective, it is preferable that the foamed particle molded body is a rectangular parallelepiped-shaped foamed block, and it is preferable that the molded body has a thickness of 400 mm or more, more preferably 450 mm or more, and even more preferably 500 mm or more. The thickness of the above-mentioned molded body is measured as follows. First, identify the side with the shortest length among the sides of the molded body, and set the direction parallel to this side as the thickness direction. Next, on each of the four surfaces having sides along the thickness direction, set five measurement positions so that the intervals in the direction perpendicular to the thickness direction are constant, and measure the length in the thickness direction of the molded body at these measurement positions. The arithmetic mean value of the 20 thicknesses thus obtained is taken as the thickness of the molded body.

[0094] The molded body is preferably a foamed particle molded body for cutting. That is, the molded body can be suitably used for applications that are used after being subjected to cutting. As described above, the molded body formed by molding the specific foamed particles in a mold is excellent in the fusibility of the foamed particles inside the molded body and has good machinability. Therefore, even when the molded body is subjected to cutting, the occurrence of fuzzing and the dropping of foamed particles are suppressed, and a molded body with a good surface is obtained.

[0095] The molded body can be suitably used as a lost mold in the full mold casting method. The full mold casting method is a casting method in which a lost mold is buried in a mold, and then molten metal is poured into the lost mold to replace the lost mold with the molten metal while performing casting. When casting a metal product by the full mold casting method, the surface shape of the lost mold is reflected in the metal product. Therefore, in order to obtain a metal product with a good surface, it is desirable that the surface of the lost mold is smooth.

[0096] On the other hand, as described above, the molded body has less fluffing due to cutting and less generation of falling of expanded particles during cutting, and has a good surface after cutting. Further, the molded body is also excellent in flammability. Therefore, by using a machined product obtained by machining the molded body as a lost mold, a metal product having a good surface can be easily obtained.

Example

[0097] Examples of the method for producing the expandable styrene resin particles will be described. The polyethylene wax used in this example is as follows. A1: "Acculin1000" manufactured by THE INTERNATIONALGROUP, INC. (IGI) A2: "Acculin850" manufactured by IGI A3: "Acculin725" manufactured by IGI A4: "Polyethylene Wax 1000" manufactured by Toyochem Co., Ltd. A5: "Acculin500" manufactured by IGI A6: "Acculin2000" manufactured by IGI

[0098] Table 1 shows various properties of the above-mentioned polyethylene waxes.

[0099]

Table 1

[0100] The measurement methods of the physical properties of the polyethylene waxes shown in Table 1 are as follows.

[0101] · Number average molecular weight Mn, weight average molecular weight Mw, and polydispersity Mw / Mn The number average molecular weight Mn and weight average molecular weight Mw of the polyethylene wax were measured by gel permeation chromatography (GPC method) using polystyrene as a standard substance. HLC-8321GPC / HT manufactured by Tosoh Corporation was used to obtain the chromatogram. The polyethylene wax as the measurement sample was dissolved in o-dichlorobenzene (o-DCB) at 145 °C, and then filtered to prepare a sample solution with a concentration of 1 g / L. Next, using a column in which one TSKguardcolumn SuperH-H and two TSK-GEL GMHHR-H(S)HT were connected in series, with the eluent: o-dichlorobenzene (o-DCB), o-dichlorobenzene (o-DCB) flow rate: 1.0 ml / min, column temperature: 145 °C as the separation conditions, the measurement sample was separated by gel permeation chromatography (GPC) according to the difference in molecular weight to obtain a chromatogram. Then, based on the calibration curve prepared using standard polystyrene, the retention time in the chromatogram was converted to molecular weight to obtain a differential molecular weight distribution curve. The weight average molecular weight of the measurement sample was calculated from this differential molecular weight distribution curve.

[0102] ·Thermal properties The thermal properties of the polyethylene wax such as the melting point and heat of crystallization were measured based on the DSC curve obtained according to JIS K7121-1987 or JIS K7122-1987. Specifically, the state adjustment of the polyethylene wax was carried out according to "(2) When measuring the melting temperature after performing a certain heat treatment". In the state adjustment, first, the polyethylene wax was heated from 0 °C to 150 °C at a heating rate of 10 °C / min, and then the temperature of 150 °C was held for 10 minutes to melt the polyethylene wax. After the state adjustment was carried out as above, the polyethylene wax was cooled from 150 °C to 0 °C at a cooling rate of 10 °C / min, and a DSC curve during cooling was obtained. Also, after cooling the polyethylene wax which also served as state adjustment, the polyethylene wax was heated from 0 °C to 150 °C at a heating rate of 10 °C / min, and a DSC curve during the second temperature rise was obtained.

[0103] Based on the DSC curve during cooling obtained as described above, the crystallization peak temperature Tpc, the heat of crystallization, the half-width of the crystallization peak, the crystallization start temperature Tic, and the crystallization end temperature Tec were determined. The crystallization peak temperature Tpc is the temperature at the apex of the crystallization peak in the said DSC curve, and the heat of crystallization is a value calculated from the peak area of the crystallization peak.

[0104] The half-width of the crystallization peak is the temperature difference between the temperature corresponding to the 1 / 2 crystallization peak height position on the high-temperature side and the temperature corresponding to the 1 / 2 crystallization peak height position on the low-temperature side in the DSC curve during cooling. The crystallization end temperature Tec is the intersection point between the straight line obtained by extending the baseline on the low-temperature side of the crystallization peak in the said DSC curve to the high-temperature side and the tangent line drawn so that the gradient is maximum on the curve on the low-temperature side of the crystallization peak. The crystallization start temperature Tic is the intersection point between the straight line obtained by extending the baseline on the high-temperature side of the crystallization peak in the said DSC curve to the low-temperature side and the tangent line drawn so that the gradient is maximum on the curve on the high-temperature side of the crystallization peak.

[0105] Note that the baseline of the crystallization peak described above is the line segment connecting the point of [crystallization start temperature + 10°C] and the point of [crystallization end temperature - 10°C] on the DSC curve. Also, the crystallization peak height is the height from the baseline to the apex of the crystallization peak, and two points on the DSC curve where the height from the baseline is 1 / 2 of the crystallization peak height were defined as the 1 / 2 crystallization peak height positions.

[0106] Also, based on the DSC curve during the second heating obtained by the operation described above, the melting point was determined. Note that the melting point is the temperature at the apex of the melting peak that appears on the said DSC curve.

[0107] · Cumulative 10% diameter, cumulative 50% diameter, cumulative 90% diameter Based on the volume-based particle size distribution, the cumulative 10% diameter (i.e., d10), cumulative 50% diameter (i.e., d50), and cumulative 90% diameter (i.e., d90) of the polyethylene wax were calculated. Also, Table 1 shows the value obtained by dividing the difference between the cumulative 90% diameter and the cumulative 10% diameter by the cumulative 50% diameter. For the measurement of the particle size distribution, a particle size distribution measuring device ("Millitrack JPA" manufactured by Nikkiso Co., Ltd.) was used.

[0108] (Example 1) The method for producing the foamed polystyrene resin particles in this example is as follows. An autoclave with an internal volume of 756 L equipped with a stirrer was used as a closed container, and 300 kg of deionized water, 0.76 kg of tricalcium phosphate, 0.1 kg of disodium hydrogen phosphate, and 0.003 kg of potassium persulfate were charged into the autoclave. Then, while stirring the contents of the autoclave, 0.302 kg of polyethylene wax as a bubble regulator, 1.84 kg of a plasticizer, a polymerization initiator, and 252 kg of styrene were charged into the autoclave. The type of the bubble regulator, the ratio of the addition amount of the bubble regulator to styrene, and the ratio of the addition amount of the plasticizer to styrene are as shown in Table 2. As the polymerization initiator, 0.75 kg of benzoyl peroxide ("Niper (registered trademark) BW" manufactured by NOF Corporation) and 0.54 g of t-butylperoxy 2-ethylhexyl monocarbonate ("Perbutyl (registered trademark) E" manufactured by NOF Corporation) were used in combination. Also, as the plasticizer, liquid paraffin ("RCM-S" manufactured by Sanko Chemical Industries, Ltd.) was used.

[0109] After stirring the contents of the autoclave at room temperature for 30 minutes, the pre-polymerization step was carried out. In the pre-polymerization step, first, the temperature inside the autoclave was raised to 90 °C over one and a half hours. After the temperature inside the autoclave reached 90 °C, this temperature was maintained for 270 minutes. Next, the temperature inside the autoclave was heated to 96 °C over 25 minutes and this temperature was maintained for 110 minutes. After the above pre-polymerization step was completed, the post-polymerization step was carried out following the pre-polymerization step. In the post-polymerization step, the temperature inside the autoclave was raised to 120 °C over one hour and 30 minutes and this temperature was maintained for 100 minutes. After the above post-polymerization step was completed, the temperature inside the autoclave was cooled to 25 °C over 4 hours. Thus, the styrene inside the autoclave was polymerized.

[0110] Also, in this example, the impregnation of the blowing agent into the styrene resin particles was carried out during the polymerization of styrene. More specifically, when 300 minutes had elapsed since the temperature inside the autoclave reached 90 °C, the supply of the blowing agent into the autoclave was started and the blowing agent was supplied over 80 minutes. As the blowing agent, 4.7 kg of pentane (a mixture of 80% normal pentane and 20% isopentane) and 19.4 kg of butane (a mixture of about 70% by mass of normal butane and about 30% by mass of isobutane) were used in combination. The ratio of the addition amount of the blowing agent to the styrene monomer is as shown in Table 2. In Table 2, normal pentane is described as "nC5", isopentane as "iC5", and butane as "mC4".

[0111] By the above operations, expandable styrene resin particles were produced. The polymerization conversion rate at the end of the pre-polymerization step in this example was 99%.

[0112] After the cooling was completed, the expandable styrene resin particles were taken out from the autoclave. After dehydrating and washing the expandable styrene resin particles using a centrifuge, the moisture adhering to the surface of the expandable styrene resin particles was removed using an air flow dryer.

[0113] Also, in this example, the surface of the expandable polystyrene resin particles was coated with a surface coating agent. Specifically, 0.088 parts by mass of zinc stearate, 0.056 parts by mass of glycerin monostearate, 0.004 parts by mass of talc, and 0.052 parts by mass of an antistatic agent (「Resistat (registered trademark) PE132」manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.025 parts by mass of dimethylpolysiloxane, and 0.02 parts by mass of glycerin were added to 100 parts by mass of the expandable polystyrene resin particles, and the surface of the expandable polystyrene resin particles was coated with a surface coating agent containing these components.

[0114] Further, after coating the surface of the expandable polystyrene resin particles with a surface coating agent, a drying treatment was performed using an air current dryer to heat the expandable polystyrene resin particles at a temperature of 50 °C for 90 minutes to remove excess moisture and the physical foaming agent.

[0115] (Example 2, Example 3) The method for producing expandable polystyrene resin particles in Example 2 and Example 3 is the same as that in Example 1, except that the addition amount of polyethylene wax was changed as shown in Table 2, and the mixture of normal pentane and isopentane in the foaming agent was changed to isopentane.

[0116] (Example 4) The method for producing expandable polystyrene resin particles in Example 4 is the same as that in Example 1, except that 4.7 kg of pentane, 16.4 kg of butane, and 3 kg of isobutane were used as the foaming agent. In Table 2, isobutane is described as 「iC4」.

[0117] (Example 5) The method for producing expandable polystyrene resin particles in Example 5 is the same as that in Example 1, except that the particle size distribution and addition amount of polyethylene wax were changed as shown in Table 2, and the mixture of normal pentane and isopentane in the foaming agent was changed to isopentane.

[0118] (Example 6) The method for producing the expandable polystyrene resin particles of Example 6 is the same as that of Example 1, except that the type of polyethylene wax is changed as shown in Table 3 and the mixture of normal pentane and isopentane in the blowing agent is changed to isopentane.

[0119] (Example 7) The method for producing the expandable polystyrene resin particles of Example 7 is the same as that of Example 1, except that the type of polyethylene wax is changed as shown in Table 3 and the mixture of normal pentane and isopentane in the blowing agent is changed to isopentane.

[0120] (Comparative Examples 1 to 3) The methods for producing the expandable polystyrene resin particles of Comparative Examples 1 to 3 are the same as that of Example 1, except that the type and amount of polyethylene wax added are changed as shown in Table 4 and the mixture of normal pentane and isopentane in the blowing agent is changed to isopentane.

[0121] (Comparative Example 4) The method for producing the expandable polystyrene resin particles of Comparative Example 4 is the same as that of Example 1, except that no polyethylene wax is added and the mixture of normal pentane and isopentane in the blowing agent is changed to isopentane.

[0122] (Comparative Example 5) The method for producing the expandable polystyrene resin particles of Comparative Example 5 is the same as that of Example 1, except that the amount of polyethylene wax added is changed as shown in Table 4 and the mixture of normal pentane and isopentane in the blowing agent is changed to isopentane.

[0123] The properties of the expandable polystyrene resin particles obtained as above are shown in Tables 2 to 4. The evaluation methods for the properties shown in Tables 2 to 4 are as follows. Also, the content of polyethylene wax with respect to 100 parts by mass of the styrene resin in the expandable polystyrene resin particles was calculated from the amount of polyethylene wax added with respect to 100 parts by mass of the styrene monomer during polymerization.

[0124] ·Average particle diameter The average particle diameter of the expandable particles is the cumulative 63% diameter (i.e., d63) calculated based on the particle size distribution on a volume basis. For the measurement of the particle size distribution, a particle size distribution measuring device ("Millitrack JPA" manufactured by Nikkiso Co., Ltd.) was used.

[0125] ·Moisture content The moisture content of the expandable styrene resin particles was measured using a Karl Fischer moisture meter. Specifically, approximately 0.28 g of expandable styrene resin particles were precisely weighed as a sample. The sample was heated at 160°C using a moisture vaporization device ("CHK-501" manufactured by Kyoto Electronics Industry Co., Ltd.) to vaporize the moisture in the sample, and the vaporized moisture was led to a Karl Fischer moisture meter ("MKC-610" manufactured by Kyoto Electronics Industry Co., Ltd.) to measure the moisture content in the sample. The measurement of the moisture content was performed by the coulometric titration method.

[0126] ·Volatile content Approximately 1 g of expandable styrene resin particles were precisely weighed as a sample. The sample was dried in a hot air dryer set at 120°C for 4 hours. After cooling this sample to room temperature, the mass of the dried sample was measured. The value obtained by expressing the ratio of the mass reduction amount (unit: g) due to drying to the mass of the sample before drying (unit: g) as a percentage was defined as the total volatile content (unit: mass %), and the value obtained by subtracting the moisture content (unit: mass %) obtained by the method described above from the total volatile content was defined as the volatile content (unit: mass %).

[0127] ·Weight average molecular weight of styrene resin The weight average molecular weight of the styrenic resin that constitutes the surface layer of the expandable particles, expanded particles, and expanded particles was measured by gel permeation chromatography (GPC method) using polystyrene as a reference substance. HLC-8320GPC EcoSEC manufactured by Tosoh Corporation was used to obtain the chromatogram. As a measurement sample, any one of the expandable particles, expanded particles, or the surface layer of the expanded particles was dissolved in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1% by mass. Then, using a column in which one TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H were connected in series, with the eluent: tetrahydrofuran (THF) and a THF flow rate of 0.6 ml / min as the separation conditions, the measurement sample was separated by gel permeation chromatography (GPC) according to the difference in molecular weight to obtain a chromatogram. Then, using the calibration curve prepared with standard polystyrene, the retention time in the chromatogram was converted to molecular weight to obtain a differential molecular weight distribution curve. The weight average molecular weight of the measurement sample was calculated from this differential molecular weight distribution curve.

[0128] · Content of styrene The content of unreacted styrene in the expandable particles was measured using a headspace gas chromatography mass spectrometer. Specifically, three standard solutions were prepared such that the styrene concentration in DMF was 5 ppm by mass, 50 ppm by mass, or 500 ppm by mass. 0.2 g of the standard solution was precisely weighed into a 20 ml vial, 1 ml of DMF was added, and the vial was sealed. The gas phase part was measured by a gas chromatography mass spectrometer, and a calibration curve was created from the obtained chromatogram. Next, 0.2 g of the expandable particles was precisely weighed and placed in a 20 ml vial together with 1 ml of DMF and sealed. This vial was held at room temperature for one day to completely dissolve the expandable particles in DMF. Then, the gas phase part of the vial was measured by a gas chromatography mass spectrometer. The content of unreacted styrene in the expandable particles was determined from the obtained chromatogram and the previously created calibration curve. In the measurement of the styrene content, when the content of unreacted styrene in the expandable particles was 1000 ppm by mass or less, it was determined that the amount of unreacted styrene in the expandable particles was sufficiently reduced.

[0129] The measurement conditions for gas chromatography-mass spectrometry were as follows. Gas chromatography-mass spectrometer: Shimadzu Corporation GCMS-QP2020 Headspace sampler: Shimadzu Corporation HS-20 Capillary column: GL Sciences Inc. Stabilwax, inner diameter 0.32 mm, length 30 m Headspace sampler heat preservation conditions: 90 °C, 1 hour Column temperature: 50 °C × 2 minutes → (heating rate: 10 °C / min) → 90 °C → (heating rate: 5 °C / min) → 120 °C → (heating rate: 20 °C / min) → 230 °C × 2 minutes Ion source temperature: 200 °C Carrier gas: helium, column flow rate 2 ml / min Split ratio: 1 / 10

[0130] · Foaming property The foaming property of the foaming polystyrene resin particles was evaluated based on the bulk density of the foamed particles when the foaming particles were foamed using a shelf-type foamer. Specifically, in the shelf-type foamer, the foaming polystyrene resin particles were heated for 270 seconds using steam at a gauge pressure of 3 kPa (G) to foam the foaming polystyrene resin particles and produce foamed particles. These foamed particles were air-dried for a whole day and night. Next, the foamed particles were filled into a graduated cylinder, and the filling height of the foamed particles was stabilized at the position of the 1 L mark. Next, the mass (unit: g) of the foamed particles in the graduated cylinder was measured. By performing unit conversion on the mass (unit: g / L) of the foamed particles per unit bulk volume of 1 L thus obtained, the bulk density (unit: kg / m 3 ) was calculated. In the "Foaming property" column of Tables 2 to 4, the bulk density of the foamed particles when foamed using a shelf-type foamer was described.

[0131] Next, expandable polystyrene resin particles with the bulk densities shown in Tables 2 to 4 were produced by expanding the expandable polystyrene resin particles of the examples and comparative examples using a pressure batch foaming machine ("DYH-1000" manufactured by DAISEN Co., Ltd.). Various properties of these expanded particles are shown in Tables 2 to 4. The evaluation methods for the various properties shown in Tables 2 to 4 are as follows. In addition, the content of polyethylene wax with respect to 100 parts by mass of the styrene-based resin in the expanded particles was calculated from the addition amount of polyethylene wax with respect to 100 parts by mass of the styrene-based monomer during polymerization.

[0132] · Bulk density of expanded particles The expanded particles were filled into a graduated cylinder, and the filling height of the expanded particles was stabilized at the position of the 1 L mark. Next, the mass (unit: g) of the expanded particles in the graduated cylinder was measured. By converting the mass (unit: g / L) of the expanded particles per unit bulk volume of 1 L obtained in this way, the bulk density (unit: kg / m 3 ) was calculated.

[0133] · Amount of residual blowing agent After dissolving the expandable particles in dimethylformamide (DMF), gas chromatography analysis of the solution was performed to measure the content of chain aliphatic hydrocarbons in the expandable particles. Then, the total content of the chain aliphatic hydrocarbons was taken as the content of the blowing agent.

[0134] Quantification of the blowing agent by gas chromatography was specifically carried out according to the following procedure. First, approximately 5 g of cyclopentanol was accurately weighed to the third decimal place in a 100 mL volumetric flask, and DMF was added to make the total volume 100 mL. This DMF solution was further diluted 100-fold with DMF to obtain an internal standard solution. Next, approximately 1 g of the foaming particles to be measured was accurately weighed to the third decimal place. After dissolving the accurately weighed foaming particles in approximately 18 mL of DMF, 2 mL of the internal standard solution was accurately added with a whole pipette to obtain a sample solution. 1 μL of this sample solution was introduced into a gas chromatography analyzer with a microsyringe to obtain a chromatogram. From the obtained chromatogram, the peak areas of each blowing agent component and the internal standard were determined, and the concentration of each component was determined by the following formula (4). Concentration of each component (mass%) = [(Wi / 10000)×2]×[An / Ai]×Fn÷Ws×100···(4)

[0135] The meanings of the symbols in the above formula (4) are as follows. Wi: Mass of cyclopentanol in the internal standard solution (unit: g) Ws: Mass of the foaming particles dissolved in DMF (unit: g) An: Peak area of each blowing agent component calculated from the chromatogram Ai: Peak area of the internal standard substance calculated from the chromatogram Fn: Correction factor of each blowing agent component obtained from the calibration curve prepared in advance

[0136] In addition, the detailed analysis conditions in gas chromatography were as follows. Analyzer: Gas chromatograph GC-6AM manufactured by Shimadzu Corporation Detector: FID (hydrogen flame ionization detector) Column material: Glass column with an inner diameter of 3 mm and a length of 5000 mm Column packing: [Liquid phase name] FFAP (free fatty acid), [Liquid phase impregnation rate] 10 mass%, [Carrier name] Diatomaceous earth for gas chromatography Chomasorb W, [Carrier particle size] 60 / 80 mesh, [Carrier treatment method] AW-DMCS (water washing, firing, acid treatment, silane treatment), [Filling amount] 90 mL Inlet temperature: 250 °C Column temperature: 120 °C Detector temperature: 250 °C Carrier gas: N2, flow rate 40 ml / min

[0137] · Average circularity and average aspect ratio of the foamed particles Using a particle size distribution measuring device "Millitrack JPA" manufactured by Nikkiso Co., Ltd., the average circularity and average aspect ratio of the foamed particles were measured. Specifically, first, approximately 5000 foamed particles were allowed to fall freely from the sample feeder of the measuring device, and the projection image was captured by a CCD camera. Next, the average circularity and average aspect ratio were obtained by sequentially performing arithmetic processing and combining processing on the captured image information.

[0138] · Average diameter, standard deviation, and coefficient of variation of the bubbles in the foamed particles Using 10 randomly selected foamed particles, the average diameter L of the bubbles in the foamed particles was calculated by the method described above av , standard deviation L sd and coefficient of variation L cv were calculated. As an example, Fig. 1 shows a cross-sectional photograph of the foamed particles E2 in Example 2, Fig. 2 shows a cross-sectional photograph of the foamed particles C1 in Comparative Example 1, and Fig. 3 shows a cross-sectional photograph of the foamed particles C2 in Comparative Example 2

[0139] · Average value of the surface layer bubble diameter of the foamed particles Using 10 randomly selected foamed particles, the average value of the bubble diameters of the bubbles existing on the outermost surface of the foamed particles was calculated by the method described above

[0140] Next, a foamed particle molded body was produced by molding the foamed particles obtained using a pressure batch foaming machine in the following manner. First, the foamed particles were aged in a constant temperature chamber at 23 °C for 1 day. Next, the foamed particles were filled into the mold of an EPS block molding machine ("VS-2000" manufactured by DAISEN Co., Ltd.). As the mold, a mold having a rectangular parallelepiped cavity with a length of 2025 mm, a width of 1020 mm, and a thickness of 520 mm was used

[0141] After the filling of the foamed particles into the mold was completed, the inside of the mold was evacuated. Then, steam was injected into the mold through a steam injection hole on one side in the thickness direction of the cavity to preheat the foamed particles in the mold. Thereafter, the styrene-based resin foamed particles in the mold were main-heated by injecting steam through the steam injection holes on both sides in the thickness direction of the cavity, and the foamed particles were fused to each other while being secondarily foamed. In addition, when injecting steam into the mold, the injection amount was controlled so that the surface pressure received by the mold became 0.09 MPa.

[0142] After the main heating was completed, the molded body in the mold was cooled until the surface pressure received by the mold became -0.005 MPa. Then, when the surface pressure reached -0.005 MPa, the cooling was stopped and the molded body was removed from the mold. The molded body removed from the mold was dried in a drying chamber at a temperature of 60 °C for 1 day, and then further cured in a constant temperature chamber at a temperature of 23 °C for 1 day.

[0143] The various properties of the molded body obtained as described above are shown in Tables 2 to 4. The evaluation methods for the various properties shown in Tables 2 to 4 are as follows.

[0144] · Molded body density The density (unit: kg / m 3 ) of the molded body was calculated by dividing the mass (unit: kg) of the molded body by the volume (unit: m 3 ) calculated based on its outer dimensions.

[0145] · Fusing rate The molded body was divided into nine equal parts in the thickness direction to produce nine thin plates. The thin plate located at the center in the thickness direction among these thin plates was bent and broken so as to be approximately equally divided in the longitudinal direction. Thereafter, the fracture surface was observed, and the number of foamed particles whose foamed particle itself was broken (material fracture) and the number of foamed particles peeled between the interfaces of the foamed particles were respectively measured. Then, the ratio of the number of foamed particles that were materially fractured to the total number of foamed particles present on the fracture surface was calculated, and the value expressed as a percentage was defined as the fusing rate (unit: %). In the evaluation of the fusing rate, a molded body with a fusing rate of 80% or more was determined to be a molded body with a good internal fusing state.

[0146] ·Maximum drum shrinkage A straightedge was brought into contact with the end faces in the thickness direction of the molded body, that is, the faces surrounded by the sides of 2025 mm in length and 1020 mm in width, and the size of the gap from the straightedge to the surface of the molded body was measured at various positions. Then, the maximum value of this gap was defined as the maximum drum shrinkage (unit: mm). In the measurement of the maximum drum shrinkage, a molded body with a maximum drum shrinkage of 5 mm or less was judged to be a molded body in which excessive drum shrinkage did not occur and a molded body having a desired shape was obtained.

[0147] ·Machinability in cutting A plate-shaped test piece with a length of 500 mm, a width of 300 mm, and a thickness of 55 mm was cut out from the molded body. The following cutting process was performed on this plate-shaped test piece to form the shapes shown in FIGS. 4 and 5. Note that an NC router (“NCN8200” manufactured by Shojida Iron Works Co., Ltd.) was used for the cutting process. Also, the rotational speed of the tool was 10,000 rpm, and the feed rate of the tool was 6,000 mm / min.

[0148] As shown in FIGS. 4 and 5, the test piece 1 after cutting has an upper cutting portion 2 formed on one side in the longitudinal direction, a lower cutting portion 4 formed on the other end side in the longitudinal direction and cut deeper than the upper cutting portion 2, and an inclined surface 3 existing between the upper cutting portion 2 and the lower cutting portion 4. The upper cutting portion 2 and the lower cutting portion 4 each have a horizontal bottom surface 21, 41 and side surfaces 22, 42 surrounding the periphery of the bottom surfaces 21, 41. The side surface 22 of the upper cutting portion 2 is formed by using a six-flute square end mill with a diameter of 20 mm and lowering the edge of the end mill by 25 mm at a time from the surface of the test piece before cutting. Also, the bottom surface 21 of the upper cutting portion 2 is formed by moving the above-mentioned square end mill in a path that spreads outward in a square shape from the center of the surface to be cut in the test piece before cutting. Note that the inner dimension of the upper cutting portion 2 in the longitudinal direction of the molded body is 120 mm, and the inner dimension of the upper cutting portion 2 in the lateral direction of the molded body is 135 mm.

[0149] The bottom surface 41 and the side surface 42 of the lower cutting portion 4 are formed by the same method as the upper cutting portion 2, except that the depth from the surface of the test piece before cutting is 45 mm.

[0150] As shown in FIG. 5, the inclined surface portion 3 has a bottom surface 31 formed so as to form an angle of approximately 30 degrees with respect to the bottom surface 41 of the lower cutting portion 4 from the bottom surface 21 of the upper cutting portion 2 to the bottom surface 41 of the lower cutting portion 4, and a side surface 32 erected from an edge of the bottom surface 31 that is not continuous with the upper cutting portion 2 and the lower cutting portion 4. More specifically, the inclined surface portion 3 uses a four-edge ball end mill with a diameter of 16 mm, and after forming one side surface 32a (see FIG. 4) of the two side surfaces 32 by lowering the blade of the end mill at once to a predetermined depth from the surface of the test piece before cutting, the end mill is moved in the lateral direction of the formed body to form the bottom surface 31 and the other side surface 32b. This is formed by repeating the process while changing the cutting start position in the longitudinal direction of the formed body.

[0151] After performing the cutting process as described above, the fluffing was evaluated based on the appearance of the side surface 32 of the inclined surface portion 3. In the "Fluffing" column of Tables 2 to 4, the symbol "A" was described when the small pieces of foam particles that could not be completely removed on the side surface 32 of the inclined surface portion 3 were less than 5 mm, and the symbol "B" was described when there were small pieces of 5 mm or more.

[0152] Also, the presence or absence of foam particle detachment was evaluated based on the appearance of the bottom surface 31 of the inclined surface portion 3. In the "Foam Particle Detachment" column of Tables 2 to 4, the symbol "A" was described when the number of foam particles detached from the bottom surface 31 of the inclined surface portion 3 was 5 or less, the symbol "B" when it was 6 or more and 10 or less, the symbol "C" when it was 11 or more and 15 or less, and the symbol "D" when it was 16 or more. In the evaluation of foam particle detachment, the cases of the symbols "A", "B", and "C" where the number of foam particles detached from the bottom surface 31 was 15 or less were judged as qualified because the foam particles were difficult to detach, and the case of the symbol "D" where it was 16 or more was judged as unqualified because the foam particles were easy to detach.

[0153]

Table 2

[0154]

Table 3

[0155]

Table 4

[0156] As shown in Table 2, in the production methods of Examples 1 to 7, the specific polyethylene wax is used as the nucleating agent. Further, the addition amount of the polyethylene wax is within the specific range. Therefore, according to the foamed polystyrene resin particles obtained by these examples, it is possible to easily obtain foamed particles in which the difference in bubble diameter between the bubbles present near the surface and the bubbles present inside is small and the variation in bubble diameter is small. And by molding such foamed particles in a mold, it is possible to easily obtain a molded body with less dropout of foamed particles during cutting and less fluffing after cutting.

[0157] On the other hand, as shown in Table 4, in the production method of Comparative Example 1, a polyethylene wax with a low heat of crystallization is used as the nucleating agent. Therefore, when the foamed particles obtained by the production method of Comparative Example 1 are foamed, the bubbles present near the surface tend to become small. A molded body formed by molding such foamed particles is inferior in machinability because dropout of foamed particles easily occurs during cutting and fluffing also easily occurs after cutting.

[0158] In the production method of Comparative Example 2, a polyethylene wax with a low melting point is used as the nucleating agent. Further, in the production method of Comparative Example 3, a polyethylene wax with a high melting point is used as the nucleating agent. Therefore, when the foamed particles obtained by these production methods are foamed, the variation in bubble diameter tends to become large. A molded body formed by molding such foamed particles is inferior in machinability because dropout of foamed particles easily occurs during cutting.

[0159] In the production method of Comparative Example 4, since no nucleating agent is used, when the expandable particles obtained by the production method of Comparative Example 4 are foamed, the variation in the cell diameter tends to be large. A molded article formed by molding such expandable particles in a mold is likely to cause the expandable particles to fall off during cutting, and thus has poor machinability.

[0160] In the production method of Comparative Example 5, since the addition amount of polyethylene wax is large, when the expandable particles obtained by the production method of Comparative Example 5 are foamed, the cells present near the surface tend to be small. A molded article formed by molding such expandable particles in a mold is likely to cause the expandable particles to fall off during cutting, and also likely to cause fuzzing after cutting, and thus has poor machinability.

[0161] As described above, the specific embodiments of the method for producing the expandable styrenic resin particles have been described based on the examples. However, the specific embodiments of the method for producing the expandable styrenic resin particles according to the present invention are not limited to the embodiments of the examples, and the configuration can be appropriately changed without departing from the spirit of the present invention.

Explanation of Reference Numerals

[0162] 1 Specimen 2 Upper Cutting Part 3 Inclined Surface Part 4 Lower Cutting Part

Claims

1. A method for producing expandable styrene resin particles comprising a styrene resin, a foaming agent, and polyethylene wax, comprising: a polymerization step of obtaining styrene resin particles by suspension-polymerizing a styrene monomer in the presence of polyethylene wax, wherein the melting point of the polyethylene wax is 90°C or higher and 120°C or lower, the heat of crystallization of the polyethylene wax calculated based on the DSC curve is 225 J / g or higher, and the amount of the polyethylene wax added in the polymerization step is 0.02 parts by mass or more and 0.2 parts by mass or less with respect to 100 parts by mass of the styrene monomer. A method for producing expandable styrene resin particles.

2. The method for producing expandable styrene resin particles according to claim 1, wherein the half-value width of the crystallization peak of the polyethylene wax in the DSC curve is 6°C or higher and 30°C or lower.

3. The method for producing expandable styrene resin particles according to claim 1 or 2, wherein the crystallization peak temperature of the polyethylene wax in the DSC curve is 90°C or higher and 105°C or lower.

4. Expandable styrene resin particles comprising a styrene resin, a foaming agent, and polyethylene wax, wherein the expandable styrene resin particles contain 0.02 parts by mass or more and 0.2 parts by mass or less of polyethylene wax with respect to 100 parts by mass of the styrene resin, the melting point of the polyethylene wax is 90°C or higher and 120°C or lower, and the heat of crystallization of the polyethylene wax calculated based on the DSC curve is 225 J / g or higher. Expandable styrene resin particles.

5. Styrene resin foam particles using a styrene resin as a base resin, The bulk density of the styrene resin foam particles is 15 kg / m ３ or more and 50 kg / m ３ or less, and wherein the coefficient of variation of the cell diameter of the styrene resin foam particles is 40% or less, the average value of the cell diameter of the cells present on the outermost surface of the styrene resin foam particles is 35 μm or more and 70 μm or less, the styrene resin foam particles contain polyethylene wax, the melting point of the polyethylene wax is 90°C or higher and 120°C or lower, and the heat of crystallization calculated based on the DSC curve of the polyethylene wax is 225 J / g or higher. Styrene resin foam particles.

6. The styrene resin foam particles according to claim 5, wherein the weight average molecular weight of the styrene resin exceeds 200,000 and is 280,000 or less.

7. A foam particle molded body obtained by molding the styrene resin foam particles according to claim 5 or 6 in a mold.

8. The foamed particle molded body is a rectangular parallelepiped foamed block having a thickness of 400 mm or more, and the foamed particle molded body according to claim 7.

9. The foamed particle molded body according to claim 7 or 8, wherein the foamed particle molded body is a foamed particle molded body for cutting.

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